1. Field
The present disclosure relates to a toner for developing an electrostatic image and a method of preparing the toner.
2. Description of the Related Art
Electrophotographic techniques and electrostatic recording techniques use developers that visualize electrostatic images or electrostatic latent images. Developers can be categorized into two-component developers and one-component developers. Two-component developers include toner and carrier particles. One-component developers include just toner. One-component developers can be sub-categorized into magnetic one-component developers and non-magnetic one-component developers. In this regard, magnetic one-component developers contain a magnetic component and non-magnetic one-component developers do not contain a magnetic component. Non-magnetic one-component developers generally include a plasticizer to increase fluidity of toner. An example of the emulsifier is colloidal silica. In general, as toner, colored particles prepared by dispersing a colorant such as carbon black and additives in latex and forming the dispersion product into particles are used.
Toner can be prepared using a milling method or a polymerizing method. In the milling method, a synthetic resin, a colorant, and if necessary, additives are dissolved and mixed, the mixture is milled and the resultant particles are classified to obtain particles having a desired diameter. In the polymerizing method, a polymerizable monomer, a colorant, a polymerization initiator, and if necessary, additives, such as a crosslinking agent or an antistatic agent, are homogeneously dissolved or dispersed to form a polymerizable monomer composition; the polymerizable monomer composition is dispersed with an agitator in an aqueous dispersion medium containing a dispersion stabilizer so as to form droplet particles of the polymerizable monomer composition; and then the temperature is increased and a suspension-polymerization process is performed thereon to obtain color polymerization particles having desired particle diameters, that is, polymerization toner.
Typically, for use in an image forming apparatus, toner obtained by using the milling method is often used. However, when toner is prepared by using the milling method, the particle size, geometric size distribution, and structure of the toner may not be accurately controlled, and thus, it is difficult to independently control major characteristics required to the toner, such as a electrifying characteristic, a fusing characteristic, a flowing characteristic, or a preservation characteristic.
Recently, a polymerization toner of which a particle size is easily controllable, and which does not require a complicated manufacturing process, such as a classification process, is getting attention. If a toner is prepared by polymerization, a polymerization toner having a desired particle size and a geometric size distribution may be obtainable without a milling process or a classification process. From among various polymerization methods, a toner agglomeration method using a metallic salt, such as MgCl2 or NaCl, or a polymer-type poly aluminum chloride (PAC) is proposed to uniformly control a particle size and a particle shape.
An agglomerating agent based on such metallic salts, with a certain level of reproducibility, enables the toner particle size or geometric size distribution to be controlled and enables a capsule structure to be constructed based on the introduction of a shell. Thus, toner having such features is used in practice. However, there is still a problem in uniformly controlling the particle size and shape. That is, when the particle size is equal to or greater than the center of the toner geometric size distribution, the toner size and shape are efficiently controlled. However, when the toner particle size is within a relatively small particle size range in the geometric size distribution, the toner particle has a higher circularity than a desired shape. Thus, in an electrostatic latent image process, blade cleaning may occur improperly.
Also, to obtain high gloss and wide fusing latitude of toner simultaneously, the toner structure is controlled to have a capsule shape through the agglomeration process. By doing so, surface exposure of a pigment and a releasing agent is suppressed, thereby contributing to uniform electrification, flowability, and thermal preservation characteristics. An offset-resistant property of toner is a critical factor in securing a stable fusing latitude, and is closely related to a rheology property of toner. The rheology property is dependent upon, for example, a molecular weight or a crosslinking level of a resin, or a releasing agent.